Current sensor using modulation of or change of sensitivity of magnetoresistance elements

ABSTRACT

A current sensor can indirectly measure a sensed current by directly measuring static perturbing AC magnetic fields with magnetoresistance elements, the perturbing magnetic fields generated by perturbing coils. The sensed current can be indirectly measured by modulating or changing sensitivities of the magnetoresistance elements in a way that is directly related to the sensed current.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of and claims the benefitof U.S. patent application Ser. No. 15/869,620 filed Jan. 12, 2018,which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to current sensors and, moreparticularly, to current sensors that use modulation of or change ofsensitivity of giant magnetoresistance (GMR) elements or tunnelmagnetoresistance (TMR) elements.

BACKGROUND

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. One such magnetic field sensing element is a magnetoresistance(MR) element. The magnetoresistance element has a resistance thatchanges in relation to a magnetic field experienced by themagnetoresistance element.

As is known, there are different types of magnetoresistance elements,for example, a semiconductor magnetoresistance element such as IndiumAntimonide (InSb), a giant magnetoresistance (GMR) element, ananisotropic magnetoresistance element (AMR), and a tunnelingmagnetoresistance (TMR) element, also called a magnetic tunnel junction(MTJ) element.

Of these magnetoresistance elements, the GMR and the TMR elementsoperate with spin electronics (i.e., electron spins) where theresistance is related to the magnetic orientation of different magneticlayers separated by nonmagnetic layers. In spin valve configurations,the resistance is related to an angular direction of a magnetization ina so-called “free-layer” relative to another layer so-called “referencelayer.” The free layer and the reference layer are described more fullybelow.

The magnetoresistances element may be used as a single element or,alternatively, may be used as two or more magnetoresistance elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses one or more magnetic field sensing elements, generallyin combination with other circuits. In a typical magnetic field sensor,the magnetic field sensing element and the other circuits can beintegrated upon a common substrate, for example, a semiconductorsubstrate. In some embodiments, the magnetic field sensor can alsoinclude a lead frame and packaging.

Magnetic field sensors are used in a variety of applications, including,but not limited to, an angle sensor that senses an angle of a directionof a magnetic field, a current sensor that senses a magnetic fieldgenerated by a current carried by a current-carrying conductor, amagnetic switch that senses the proximity of a ferromagnetic object, arotation detector that senses passing ferromagnetic articles, forexample, magnetic domains of a ring magnet or a ferromagnetic target(e.g., gear teeth) where the magnetic field sensor is used incombination with a back-biased or other magnet, and a magnetic fieldsensor that senses a magnetic field density of a magnetic field.

Various parameters characterize the performance of magnetic fieldsensors and magnetic field sensing elements. With regard to magneticfield sensing elements, the parameters include sensitivity, which is thechange in the output signal of a magnetic field sensing element inresponse to a magnetic field, and linearity, which is the degree towhich the output signal of a magnetic field sensor varies linearly(i.e., in direct proportion) to the magnetic field. The parameters alsoinclude offset, which describes and output from the magnetic fieldsensing element that is not indicative of zero magnetic field when themagnetic field sensor experiences a zero magnetic field.

GMR and TMR elements are known to have a relatively high sensitivity,compared, for example, to Hall effect elements. Thus, a current sensorthat uses GMR or TMR elements can sense smaller currents than can acurrent sensor that uses Hall effect elements.

Conventional current sensors are also known to be undesirably responsiveto external stray magnetic fields.

TMR elements are known to have a higher sensitivity than GMR elements,but at the expense of higher noise at low frequencies.

Also, it is known that some GMR and TMR elements tend to have anundesirable offset voltage, the offset voltage sensitivity changing withtemperature. Also, it is known that some GMR and TMR elements tend tochange behavior, e.g., offset voltage, after high temperature operationor storage. The offset voltage and changes of offset voltage can cause acurrent sensor that uses a GMR or TMR element to indicate a wrongcurrent.

Thus, it would be desirable to provide a current sensor that uses GMR orTMR elements, which provides a reduced effect of offset voltages,provides a reduced effect of changes of offset voltage, which provides areduced impact of external stray magnetic fields, and which caneffectively use TMR elements to obtain a higher sensitivity to currents.

SUMMARY

The present invention provides a current sensor that uses GMR or TMRelements, and which provides a reduced effect of offset voltages,provides a reduced effect of changes of offset voltage, which provides areduced impact of external stray magnetic fields, and which caneffectively use TMR elements to obtain a higher sensitivity to currents.

In accordance with an example useful for understanding an aspect of thepresent invention, a magnetic field sensor can include a firstmagnetoresistance element having a first maximum response axis andhaving a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis. The magnetic fieldsensor can also include a second magnetoresistance element having asecond maximum response axis parallel to the first maximum response axisand having a second pinning layer with a second magnetic directionperpendicular to the second maximum response axis. The magnetic fieldsensor can also include a first magnetic field generator disposedproximate to the first magnetoresistance element, the first magneticfield generator configured to generate a first AC magnetic fieldexperienced by the first magnetoresistance element and parallel to thefirst maximum response axis. The magnetic field sensor can also includea second magnetic field generator disposed proximate to the secondmagnetoresistance element, the second magnetic field generatorconfigured to generate a second AC magnetic field experienced by thesecond magnetoresistance element and parallel to the second maximumresponse axis. The magnetic field sensor can be responsive to a sensedcurrent passing through a current conductor. The current conductor caninclude a first current conductor portion disposed proximate to thefirst magnetoresistance element. The current conductor can also includea second current conductor portion disposed proximate to the secondmagnetoresistance element. The first current conductor portion can beconfigured to generate a first current conductor magnetic fieldexperienced by the first magnetoresistance element in response to thesensed current passing through the current conductor. The second currentconductor portion can be configured to generate a second currentconductor magnetic field experienced by the second magnetoresistanceelement in response to the sensed current passing through the currentconductor. The first current conductor magnetic field can beperpendicular to the first maximum response axis, and the second currentconductor magnetic field can be perpendicular to the second maximumresponse axis.

In accordance with another example useful for understanding anotheraspect of the present invention, a method of providing a magnetic fieldsensor can include generating a first AC magnetic field experienced by afirst magnetoresistance element and parallel to a first maximum responseaxis, the first magnetoresistance element having the first maximumresponse axis and having a first pinning layer with a first magneticdirection perpendicular to the first maximum response axis. The methodcan also include generating a second AC magnetic field experienced by asecond magnetoresistance element and parallel to a second maximumresponse axis, the second magnetoresistance element having the secondmaximum response axis parallel to the first maximum response axis andhaving a second pinning layer with a second magnetic directionperpendicular to the second maximum response axis. The method can alsoinclude generating a first current conductor magnetic field experiencedby the first magnetoresistance element in response to a sensed currentpassing through a current conductor. The method can also includegenerating a second current conductor magnetic field experienced by thesecond magnetoresistance element in response to the sensed currentpassing through the current conductor. The first current conductormagnetic field can be perpendicular to the first maximum response axis,and the second current conductor magnetic field can be perpendicular tothe second maximum response axis.

In accordance with another example useful for understanding anotheraspect of the present invention, a magnetic field sensor can includemeans for generating a first AC magnetic field experienced by a firstmagnetoresistance element and parallel to a first maximum response axis,the first magnetoresistance element having the first maximum responseaxis and having a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis. The magnetic fieldsensor can also include means for generating a second AC magnetic fieldexperienced by a second magnetoresistance element and parallel to asecond maximum response axis, the second magnetoresistance elementhaving the second maximum response axis parallel to the first maximumresponse axis and having a second pinning layer with a second magneticdirection perpendicular to the second maximum response axis. Themagnetic field sensor can also include means for generating a firstcurrent conductor magnetic field experienced by the firstmagnetoresistance element in response to a sensed current passingthrough a current conductor. The magnetic field sensor can also includemeans for generating a second current conductor magnetic fieldexperienced by the second magnetoresistance element in response to thesensed current passing through the current conductor. The first currentconductor magnetic field can be perpendicular to the first maximumresponse axis, and the second current conductor magnetic field can beperpendicular to the second maximum response axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a block diagram showing four TMR elements, each with aplurality of TMR pillars, proximate to a current conductor;

FIG. 2 is a block diagram showing one TMR pillar, two coils, andmagnetic field directions associated with the two coils;

FIG. 3 is a block diagram showing an illustrative GMR element havinglayers;

FIG. 3A is a block diagram showing an illustrative TMR element havinglayers;

FIG. 4 is a block diagram showing an expanded view of two of the fourTMR elements of FIG. 1 and showing positions of the two coils of FIG. 2;

FIG. 5 is a block diagram showing a current sensor having the four TMRelements and the current conductor of FIG. 1, and also showing asubstrate proximate to the current conductor;

FIG. 6 is a schematic diagram showing two TMR elements or two GMRelements coupled to a differential amplifier to generate a differencesignal;

FIG. 7 is a schematic diagram showing four TMR elements or four GMRelements coupled in a bridge arrangement to generate a differencesignal;

FIG. 8 is a graph showing a variety of signals that can be generated bya current sensor having the arrangement of FIGS. 5-7;

FIG. 9 is a graph showing a variety of signals generated by a currentsensor having the arrangement of FIG. 5-7 and having an amplitudedetector resulting in amplitudes of the signals of FIG. 8;

FIG. 10 is a schematic diagram of an illustrative current sensor havingtwo TMR or GMR elements and two amplitude detector circuits and with anon-feedback arrangement;

FIG. 11 is a schematic diagram of an illustrative current sensor havingtwo TMR or GMR elements and two amplitude detector circuits and with afeedback arrangement;

FIG. 12 is a schematic diagram of an illustrative current sensor havingtwo TMR or GMR elements and two different amplitude detector circuitsand with a non-feedback arrangement;

FIG. 13 is a schematic diagram of an illustrative current sensor havingfour TMR or GMR elements, arranged in two full bridges, and twoamplitude detector circuits and with a non-feedback arrangement;

FIG. 14 is a schematic diagram of an illustrative current sensor havingfour TMR or GMR elements, arranged in one full bridge, and the twodifferent amplitude detector circuits of FIG. 12 and with a non-feedbackarrangement; and

FIG. 15 is a schematic diagram of an illustrative current sensor havingfour TMR or GMR elements, arranged in one full bridge, and the twodifferent amplitude detector circuits of FIG. 12 and with a feedbackarrangement.

DETAILED DESCRIPTION

Before describing the present invention, it should be noted thatreference is sometimes made herein to GMR or TMR elements havingparticular shapes (e.g., yoke shaped or pillar shaped). One of ordinaryskill in the art will appreciate, however, that the techniques describedherein are applicable to a variety of sizes and shapes.

As used herein, the term “anisotropy” or “anisotropic” refer to amaterial that has different properties according to direction in thematerial. A magnetoresistance element can have a particular axis ordirection to which the magnetization of a ferromagnetic or ferrimagneticlayer tends to orientate when it does not experience an additional,external, magnetic field. An axial anisotropy can be created by acrystalline effect or by a shape anisotropy, both of which can allow twoequivalent directions of magnetic fields. A directional anisotropy canalso be created in an adjacent layer, for example, by anantiferromagnetic layer, which allows only a single magnetic fielddirection along a specific axis in the adjacent layer.

In view of the above, it will be understood that introduction of ananisotropy in a magnetic layer results in forcing the magnetization ofthe magnetic layer to be parallel to that anisotropy in the absence ofan external field. In the case of a GMR or TMR element, a directionalanisotropy provides an ability to obtain a coherent rotation of themagnetization in a magnetic layer in response, for example, to anexternal magnetic field, which has the property of suppressing thehysteresis behavior of the corresponding element.

As described above, as used herein, the term “magnetic field sensingelement” is used to describe a variety of different types of electronicelements that can sense a magnetic field. A magnetoresistance element isbut one type of magnetic field sensing element.

As is known, there are different types of magnetoresistance elements,for example, a semiconductor magnetoresistance element such as IndiumAntimonide (InSb), a giant magnetoresistance (GMR) element, ananisotropic magnetoresistance element (AMR), and a tunnelingmagnetoresistance (TMR) element, also called a magnetic tunnel junction(MTJ) element.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnet,and a magnetic field sensor that senses a magnetic field density of amagnetic field.

The terms “parallel” and “perpendicular” may be used in various contextsherein. It should be understood that the terms parallel andperpendicular do not require exact perpendicularity or exactparallelism, but instead it is intended that normal manufacturingtolerances apply, which tolerances depend upon the context in which theterms are used. In some instances, the term “substantially” is used tomodify the terms “parallel” or “perpendicular.” In general, use of theterms “substantially” and the term “about” reflect angles that arewithin manufacturing tolerances, for example, within +/−ten degrees.

Structures and methods described herein apply to both GMR and TMRmagnetoresistance elements, but, only TMR elements are used in examplesherein. However, it should be appreciated that the same or similarstructures and methods can apply to other spin electronicsmagnetoresistance elements, either now known or later discovered. Thisincludes, in particular, oxide based spin electronics structures.

Referring to FIG. 1, a structure 100, which can be part of a currentsensor described below in conjunction with FIG. 5, can include a currentconductor 102. The current conductor can be formed as an open loop forwhich current travels in two different directions. The structure 100 canalso include four TMR elements 104, 106, 108, 110. Each TMR element canbe comprised of a plurality of so-called “pillars.” Four pillars areshown for each one of the TMR elements 104, 106, 108, 110. However, inother embodiments each TMR element can include a different number ofpillars, fewer than or greater than four pillars. In some embodiments,each TMR element has approximately thirty pillars.

Referring now to FIG. 2, shown under the TMR elements 104, 106, 108, 110of FIG. 1, the structure 100 can include four coils, here expanded astwo coils 206, 208.

A pillar 200 can be the same as or similar to one of the pillars of theTMR elements 104, 106, 108, 110. It should be understood that the coil206 can generate a magnetic field with the direction indicated by anarrow 202, and the coil 208 can generate a magnetic field with adirection indicated by an arrow 204. The coils and the magneticdirections are described more fully in figures below.

FIGS. 3 and 3A describe illustrative GMR and TMR elements, respectively.It will be understood that TMR elements are used in various descriptionsherein. However, GMR elements can be used in place of the TMR elements.

Referring now to FIG. 3, an illustrative double pinned GMR element 300can be comprised of a stack of layers 304-326 disposed upon a surface ofa substrate 302.

It will be understood that driving current can run across the layers ofa GMR stack of layers, i.e., parallel to the surface of the substrate302. However, in some embodiments, the driving current can run throughthe layers in a direction perpendicular to the substrate 302. The GMRelement 300 can have a maximum response axis that is parallel to thesurface of the substrate and that is in a direction 328 perpendicular tozero field magnetic directions of the free layers 312, 314, and alsoparallel to the field generated by the reference layers, most notablethe pinned layer 318.

The GMR element 300 is double pinned, i.e., it has two pinning layers306, 324. A synthetic antiferromagnet (SAF) pinned layer structure 318,320, 322 is magnetically coupled to the pinning layer 324. The layers324, 322, 320, 318 are collectively referring to as reference layers.The single layer pinned layer 308 is magnetically coupled to the pinninglayer 306. The layers 306, 308 are collectively referred to bias layers.At zero external magnetic field, the free layers 312, 314 take on amagnetic alignment parallel to the bias layers 306, 308, with direction(ferromagnetic or antiferromagnetic coupling) determined by thicknessand material of the spacer layer 310.

Single pinned arrangements are also possible with one pinning layers andone pinned layer. Advantages of double pinned versus double pinnedarrangement are known.

In some embodiments, the single layer pinned layer 308 is replaced byanother SAF structure. In still other embodiments, the SAF structure318, 320, 322 is replaced by a single layer pinned layer.

As described above, in general, the GMR element 300 has a maximumresponse axis (maximum response to external fields) aligned with thearrow 328, i.e., perpendicular to bias directions experienced by thefree layers 312, 314, and parallel to magnetic fields of the referencelayers, notably pinned layer 318. Also, in general, it is rotations ofthe magnetic direction of the free layers 312, 314, caused by externalmagnetic fields that result in changes of resistance of the GMR stack300.

A conventional current sensor may directly sense magnetic fields thatare in the direction of the arrow 328, which are generated by sensedcurrents (which are not the above mentioned-currents that drive the GMRelement 300). However, it will become apparent from discussion belowthat, for embodiments herein, the sensed current generates externalmagnetic fields either into or out of the page, i.e., parallel tomagnetic fields of the pinned layers 312, 314 and parallel to magneticfields of the bias layers 306, 308. Magnetic fields in these directionsdue to sensed current (i.e., external magnetic fields) tend to increaseor decrease a sensitivity of the GMR element 300, sensitivity along thedirection 328. Essentially, the external magnetic fields parallel to themagnetic fields of the bias layers 306, 308 tend to add to or subtractfrom fields in this direction experience by the free layers 312, 314. Itwill become apparent that the sensitivity shift is sensed by circuitsand techniques herein, and thus, it is the sensitivity shift thatrepresents the sensed current.

Referring now to FIG. 3A, in which like elements of FIG. 3 are shownhaving like reference designations, an illustrative TMR element 350 canhave a stack 350 of layers 358, 306-310, 356, 354, 352, 320-326indicative of one pillar of a multi-pillar TMR element.

It will be understood that a driving current running through the TMRelement 350 runs through all of the layers of the stack, running betweenseed and cap layers 358 and 326, i.e., perpendicular to a surface of thesubstrate 302. The TMR element 350 can have a maximum response axis thatis parallel to the surface of the substrate and that is in the direction328 perpendicular to zero field magnetic directions of the free layer356, and also parallel to the bias field generated by the referencelayers, most notably in the pinned layer 352.

The TMR element 350 is double pinned, i.e., it has two pinning layers306, 324. A synthetic antiferromagnet (SAF) pinned layer structure 352,320, 322 is magnetically coupled to the pinning layer 324. The layers324, 322, 320, 352 are collectively referring to as reference layers.The single layer pinned layer 308 is magnetically coupled to the pinninglayer 306. The layers 306, 308 are collectively referred to as biaslayers. With zero external magnetic field, the free layer 356 takes on amagnetic alignment parallel to the bias layers 306, 308, with direction(ferromagnetic or antiferromagnetic coupling) determined by thicknessand material of the spacer layer 310.

In some embodiments, the single layer pinned layer 308 is replaced byanother SAF structure. In still other embodiments, the SAF structure352, 320, 322 is replaced by a single layer pinned layer.

As described above, in general, the TMR element 350 has a maximumresponse axis (maximum response to external fields) aligned with thearrow 328, i.e., perpendicular to bias directions experienced by thefree layer 356, and parallel to magnetic fields of the reference layers,notably pinned layers 352. Also, in general, it is rotations of themagnetic direction of the free layer 356 caused by external magneticfields that result in changes of resistance of the TMR element 350.

A conventional current sensor may directly sense magnetic fields thatare in the direction of the arrow 328, which are generated by sensedcurrents (which are not the above mentioned-currents that drive the TMRelement 350). However, it will become apparent from discussion belowthat, for embodiments herein, the sensed current generates externalmagnetic fields either into or out of the page, i.e., parallel tomagnetic fields of the free layer 356 and parallel to magnetic fields ofthe bias layers 306, 308. Magnetic fields in these directions due tosensed current (i.e., external magnetic field) tend to increase ordecrease a sensitivity of the TMR element 300, sensitivity along thedirection 328. Essentially, the external magnetic fields parallel to themagnetic fields of the bias layers 306, 308 tend to add to or subtractfrom fields in this direction experience by the free layer 356. It willbecome apparent that the sensitivity shift is sensed by circuits andtechniques herein, and thus, it is the sensitivity shift that representsthe sensed current.

Referring to FIG. 4, illustrative TMR elements 400 include a first TMRelement 402 and a second TMR element 404. Each one of the TMR elementsincludes a respective four TMR pillars that extend upward from a surfaceof a substrate on which the TMR elements 402, 404 are formed. Asdescribed above, a TMR element can have more than four or fewer thanfour pillars. The TMR elements 400 are the same as TMR elements 104, 106or TMR elements 108, 110 of FIG. 1, but here shown in expanded form tobetter show the coils 406, 408, which can be the same as or similar tothe coils 208, 206 of FIG. 2.

In non-feedback arrangements, the feedback coils 408 are not formed.

It will be understood that, when an AC current is applied to theperturbing coil 406, a perturbing magnetic field is generated in adirection parallel to the page and oriented between top and bottom onthe page. In contrast, when an AC or DC current is applied to thefeedback coil 408, a feedback magnetic field is generated in a directionparallel to the page and oriented between right and left on the page.

Referring again briefly to FIG. 3A, the TMR element 350 is shown in sideview, but the TMR elements 402, 404 are shown in top view. The TMRelement pillars are oriented such that the maximum response axis 328 isparallel to the perturbing magnetic fields generated by the perturbingcoil 406, i.e., between right and left on the page of FIG. 3A butbetween top and bottom on the page of FIG. 4. Accordingly, the TMRelement pillars can be oriented such that the maximum response axis 328is perpendicular to the current conductor (external) magnetic fieldsgenerated by the sensed currents 501 of FIG. 5. Also, the TMR elementpillars can be oriented such that magnetic directions of the referencelayers of the TMR element 350 are perpendicular to the current conductormagnetic fields generated by the sensed currents.

With this orientation of the TMR element pillars, the TMR elementpillars are also oriented such that a direction of bias magnetic fieldsin the bias layers 306, 308 is parallel to a feedback magnetic fieldgenerated by the feedback coil 408, i.e., into and out of the page onFIG. 3A, but between right and left on the page of FIG. 4, which is alsoparallel to, but opposing, sensed magnetic fields generated by thesensed current.

Referring again briefly to FIG. 4, when feedback is used, fieldsgenerated by the feedback coil 408 are used to oppose (and are parallelto) fields resulting from sensed current in the current conductor 102 ofFIG. 1, which are also parallel to fields in the bias layers 306, 308 ofFIG. 3A.

From the above, it should be understood that, for a circuit with nofeedback and no feedback coils 408, sensed magnetic fields resultingfrom sensed currents result in sensitivity shifts of the TMR elements400 and the sensed magnetic fields are not directly sensed. For acircuit with feedback, the feedback coil 408 can generate a feedbackmagnetic field that fully opposes the sensed magnetic field generated bythe sensed currents in a current conductor. The feedback coilarrangement can result in no sensitivity shift at the TMR elements 400.However, current in the feedback coil 408 can be indicative of asensitivity shift that would have occurred were it not for the feedbackarrangement and the feedback coil 408. The current in the feedback coilscan be indicative of the sensitivity shift that would have occurred.

Examples of circuits with and without feedback are described inconjunction with figures below. Advantages of feedback arrangementsinclude, but are not limited to, and ability to keep the TMR or GMRelement operating at a near zero magnetic field, i.e., within a linearregion of a transfer characteristic of the TMR or GMR element. Thus,nonlinearity of the measurement of the sensed magnetic field and sensedcurrent can be greatly reduced versus a non-feedback arrangement.

Advantages of using the sensitivity shifts as that which are sensed bythe sensed current and resulting sensed magnetic field are described inconjunction with figures below.

Referring now to FIG. 5, a magnetic field sensor 500 can include fourTMR elements 504, 506, 508, 510 disposed upon a substrate 510 along withan electronic circuit 512.

The magnetic field sensor can also include a current conductor 502through which a sensed current 501, Ip+, Ip− that the magnetic fieldsensor 500 is operable to measure, can flow. To avoid confusion herein,the sensed current 501 is described herein to be a DC sensed current.However, the same techniques apply to an AC measure current.

As indicated, because the current conductor 502 is an open loop, thecurrent 501 flows in two different directions Ip−, Ip+. The currentconductor 502 has two current conductor portions 502 a, 502 b. Thus, thecurrent 501 results in two different direction magnetic fieldsrepresented by arrows 503 a, 503 b.

It should be understood from discussion above that maximum response axesof the four TMR element 504, 506, 508, 510 are parallel to the long axisof the TMR elements, i.e., between top and bottom of the page, and areall in the same direction. Along this same axis, perturbing magneticfields generated by perturbing coils, e.g., 406 of FIG. 4, aregenerated.

Also, the fields in the bias layers e.g., 306, 308 of FIG. 3A, arealigned between right and left on the page of FIG. 5 and all have thesame direction. Thus, the sensed current magnetic fields 503 a, 503 bare aligned with the bias magnetic fields (between right and left) andnot with the maximum response axis (between top and bottom). Since thesensed magnetic fields 503 a, 503 b are in opposite directions,sensitivity of two of the TMR elements, e.g., 504, 506, moves in onedirection, e.g., increases, and sensitivity of the other two TMRelements, e.g., 508, 510, moves in the other direction, e.g., decreases.

In some embodiments, the current conductor 502 can be part of a leadframe of the magnetic field sensor 500, which can terminate at two of aplurality of leads in the lead frame. In other embodiments, the currentconductor 502 is not part of the magnetic field sensor, but is instead aseparate conductor, for example, a current conductor on a circuit boardto which the magnetic field senor 500 is mounted.

The TMR elements 504, 506 are labeled as left, L, and the TMR elements508, 510 are labeled right, R. The left and right designations arearbitrary, and are used to indicate that the TMR elements 504, 506experience the magnetic field 503 a that is in a different directionfrom the magnetic field 503 b experience by the TMR elements 508, 510.However, for convenience, left and right also indicate left and rightsides of FIG. 5. The different directions result from the two differentdirections in which the sensed current 501 flows in the currentconductor 502.

While the four TMR elements 504, 506, 508, 510 are shown, in otherembodiments, there can be two TMR elements, one disposed on the left andone disposed on the right. In other embodiments, there can be more thanfour TMR elements, with half on the left and half on the right.

Referring now to FIG. 6, an electronic circuit 600, used in illustrativemagnetic field sensors described in conjunction with figures below, caninclude first and second magnetoresistance elements 602, 604, e.g., TMRelements. The magnetoresistance element 602 can receive a drivingcurrent from a current source 606. The magnetoresistance element 604 canreceive a driving current from a current source 608.

Voltages 602 a, 604 a are generated by the first and secondmagnetoresistance elements 602, 604, respectively, which are responsiveto magnetic fields.

A differential amplifier 610 is coupled to the first and secondmagnetoresistance elements 602, 604. The differential amplifier 610 isoperable to generate a voltage 610 a that is a difference (U=L−R) of thevoltages 602 a, 604 a. Reasons for the difference are described inconjunction with figures below.

It should be understood that circuits described in conjunction withfigures below can instead generate a difference R-L, with minormodifications.

Referring now to FIG. 7, an electronic circuit 700, used in illustrativemagnetic field sensors described in conjunction with figures below, caninclude first, second, third, and fourth magnetoresistance elements 702,704, 706, 708, e.g., TMR elements arranged in a full bridge arrangement.The full bridge arrangement can be coupled between a voltage source 710and a reference voltage, e.g., a ground voltage.

Voltages 700 a, 700 b are generated by the full bridge, both of whichare responsive to magnetic fields. A difference between the voltages 700a, 700 b is automatically generated by the full bridge arrangement.

A differential amplifier 712 can be coupled to the full bridgearrangement. The differential amplifier 712 is operable to generate adifference signal 712 a that is also a difference of the voltages 700 a,700 b. Reasons for the difference are described in conjunction withfigures below.

Referring now to FIG. 8, graphs 800 have vertical ranges in amplitude,for example, volts in arbitrary units, and horizontal ranges in time inarbitrary units.

For clarity, the graphs 800 use sensed currents, e.g., the sensedcurrent 501 of FIG. 5, as being DC currents, in particular, I=0, I>0,and I<0. However, here and in circuits described below, it will beunderstood that the sensed currents can be AC currents.

Graph 802 is indicative of an AC signal 802 a generated by the leftmagnetoresistance element(s), e.g., one of, or both of, themagnetoresistance elements 504, 506 of FIG. 5, when the sensed current,e.g., 501 of FIG. 5, is zero. The AC part of the signal is a result ofthe perturbing magnetic field described above in conjunction with FIG.4, generated by the coil 406, which, as described above, can be alignedwith a maximum response axis of the left magnetoresistance element(s).The perturbing magnetic field can have a constant amplitude. In someembodiments, the perturbing magnetic field, and the resulting AC signal802 a can have a high frequency, e.g., one megaHertz.

Graph 804 is indicative of an AC signal 804 a generated by the rightmagnetoresistance element(s), e.g., one of or both of themagnetoresistance elements 508, 510 of FIG. 5, when the sensed current,e.g., 501 of FIG. 5, is zero. The AC part of the signal is a result ofthe perturbing magnetic field also described above in conjunction withFIG. 4, generated by the coil 406, which, as described above, can bealigned with a maximum response axis of the right magnetoresistanceelement(s).

Graph 806 shows a signal 806 a indicative of a difference between the ACsignals 802 a, 804 a. Thus, for a zero sensed current, I, the differenceis the signal 806 a with an AC amplitude of zero.

Graph 808 is indicative of an AC signal 808 a generated by the leftmagnetoresistance element(s), e.g., one of or both of themagnetoresistance elements 504, 506 of FIG. 5, in response to theperturbing magnetic field(s) generated by the perturbing coils(s), whenthe sensed current, e.g., 501 of FIG. 5, is greater than zero. The ACpart of the signal 808 a is a result of the perturbing magnetic fielddescribed above in conjunction with FIG. 4, generated by perturbingcoils proximate to the left magnetoresistance element(s), e.g., 406,which, as described above, can be parallel to a maximum response axis ofthe left magnetoresistance element(s). The signal 808 a is greater inamplitude than the signal 802 a due to an effect of the magnetic fieldgenerated by the non-zero sensed current, e.g., the magnetic field 503 agenerated by the measure current 501 of FIG. 5.

As described above in conjunction with FIG. 4, the magnetic fieldgenerated by the sensed current, in a direction parallel to magneticfields in the bias layers 306, 308 of FIG. 4, has the effect of changinga sensitivity of the left magnetoresistance element(s), here shown to bean increase of sensitivity. Thus, the magnetic field generated by thesensed current 501 has an indirect influence upon the signal 808 a.

Graph 810 is indicative of an AC signal 810 a generated by the rightmagnetoresistance element(s), e.g., one of or both of themagnetoresistance elements 508, 510 of FIG. 5, in response to theperturbing magnetic field(s) generated by the perturbing coils(s), whenthe sensed current, e.g., 501 of FIG. 5, is greater than zero. The ACpart of the signal 810 a is a result of the perturbing magnetic fielddescribed above in conjunction with FIG. 4, generated by perturbingcoils proximate to the right magnetoresistance element(s), e.g., 406,which, as described above, can be parallel to a maximum response axis ofthe right magnetoresistance element(s). The signal 810 a is lower inamplitude than the signal 804 a due to an effect of the magnetic fieldgenerated by the non-zero sensed current, e.g., the magnetic field 503 bgenerated by the sensed current 501 of FIG. 5, and which is in adirection opposite to the magnetic field 503 a.

As described above in conjunction with FIG. 4, the magnetic fieldgenerated by the sensed current, in a direction parallel to magneticfields in the bias layers 306, 308 of FIG. 4, has the effect of changinga sensitivity of the left magnetoresistance element(s), here shown to bea decrease of sensitivity. Thus, the magnetic field generated by thesensed current 501 has an indirect influence upon the signal 810 a.

Graph 812 shows a signal 812 a indicative of a difference between the ACsignals 808 a, 810 a. Thus, for a sensed current, I, greater than zero,the difference is the signal 812 a with a non-zero AC amplitude.Amplitude of the signal 812 a is indicative of an amplitude of thesensed current 501. Phase of the signal 812 a is indicative of adirection of the sensed current 501.

Graph 814 is indicative of an AC signal 814 a generated by the leftmagnetoresistance element(s), e.g., one of or both of themagnetoresistance elements 504, 506 of FIG. 5, in response to theperturbing magnetic field(s) generated by the perturbing coils(s), whenthe sensed current, e.g., 501 of FIG. 5, is less than zero. The AC partof the signal 814 a is a result of the perturbing magnetic fielddescribed above in conjunction with FIG. 4, generated by perturbingcoils proximate to the left magnetoresistance element(s), e.g., 406,which, as described above, can be parallel to a maximum response axis ofthe left magnetoresistance element(s). The signal 814 a is smaller inamplitude than the signal 802 a due to an effect of the magnetic fieldgenerated by the non-zero sensed current, e.g., the magnetic field 503 agenerated by the measure current 501 of FIG. 5, but now reversed versusfield 503 b.

As described above in conjunction with FIG. 4, the magnetic fieldgenerated by the sensed current, in a direction parallel to magneticfields in the bias layers 306, 308 of FIG. 4. has the effect of changinga sensitivity of the left magnetoresistance element(s), here shown to bea decrease of sensitivity. Thus, the magnetic field generated by thesensed current 501 has an indirect influence upon the signal 814 a.

Graph 816 is indicative of an AC signal 816 a generated by the rightmagnetoresistance element(s), e.g., one of or both of themagnetoresistance elements 508, 510 of FIG. 5, in response to theperturbing magnetic field(s) generated by the perturbing coils(s), whenthe sensed current, e.g., 501 of FIG. 5, is lesser than zero. The ACpart of the signal 816 a is a result of the perturbing magnetic fielddescribed above in conjunction with FIG. 4, generated by perturbingcoils proximate to the right magnetoresistance element(s), e.g., 406,which, as described above, can be parallel to a maximum response axis ofthe right magnetoresistance element(s). The signal 816 a is higher inamplitude than the signal 804 a due to an effect of the magnetic fieldgenerated by the non-zero sensed current, e.g., the magnetic field 503 bgenerated by the sensed current 501 of FIG. 5, and which is in adirection aligned with the magnetic field 503 a.

As described above in conjunction with FIG. 4, the magnetic fieldgenerated by the sensed current, in a direction parallel to magneticfields in the bias layers 306, 308 of FIG. 4, has the effect of changinga sensitivity of the left magnetoresistance element(s), here shown to bea decrease of sensitivity. Thus, the magnetic field generated by thesensed current 501 has an indirect influence upon the signal 814 a.

Graph 818 shows a signal 818 a indicative of a difference between the ACsignals 812 a, 812 b. Thus, for a sensed current, I, less than zero, thedifference is the signal 818 a with a non-zero AC amplitude. Amplitudeof the signal 818 a is indicative of an amplitude of the sensed current501. Phase of the signal 818 a is indicative of a direction of thesensed current 501. The signal 818 a (and 816 a, 814 a) is opposite inphase from (one hundred eighty degrees apart from) the signal 812 a,which is indicative of the different directions of the sensed current.

As described above, the graphs 800 are indicative of DC sensed magneticfields, e.g., 503 a, 503 b of FIG. 5, generated by a DC current, e.g.,501 of FIG. 5. However, the same techniques apply to AC sensed magneticfields generated by and AC sensed current. To this end, it will beunderstood that preferably, the AC sensed current has a frequency orbandwidth less than a frequency of the perturbing magnetic fields, e.g.,frequency of the signals in the graphs 800. In some embodiments, thefrequency or bandwidth of the AC sensed current is less than one half ofthe frequency of the perturbing magnetic fields. In some embodiments,the frequency or bandwidth of the AC sensed current is less than onefifth or less than one tenth of the frequency of the perturbing magneticfields.

Referring now to FIG. 9 and referring back to FIG. 8, graphs 900 show DCsignals 902 a, 904 a, 906 a, 908 a, 910 a, 912 a, 914 a, 916 a, 918 athat are indicative of AC amplitudes of the signals 802 a, 804 a, 806 a,808 a, 810 a, 812 a, 814 a, 816 a, 818 a, respectively. The signal 918 ais shown as a negative amplitude, which is indicative of the signal 818a being one hundred eighty degrees out of phase from the other signals.Compare signals 912 a and 918 a and also signals 812 a and 818 a. Thesignal 918 a with an opposite sign is an outcome of the signal 918 abeing a difference of signals 914 a and 916 a.

Reasons for the signals 902 a, 904 a, 906 a, 908 a, 910 a, 912 a, 914 a,916 a, 918 a indicative of amplitudes will become apparent in figuresbelow that describe amplitude detecting circuits.

Referring now to FIG. 10, an illustrative magnetic field sensor 1000 caninclude first and second magnetoresistance elements 1002, 1004,respectively, which are also designated left, L, and right, R,magnetoresistance elements, which can indicate left and right sides ofFIG. 5.

The first magnetoresistance element 1002 can be the same as or similarto the magnetoresistance element 602 of FIG. 6. The secondmagnetoresistance element 1004 can be the same as or similar to themagnetoresistance element 604 of FIG. 6.

The first magnetoresistance element 1002 is coupled to receive a drivingcurrent from current source 1006. The second magnetoresistance element1004 is coupled to receive a driving current from a current source 1008.A voltage signal 1002 a is generated by the first magnetoresistanceelement 1002. A voltage signal 1004 a is generated by the secondmagnetoresistance element 1004.

The first magnetoresistance element 1002 has a maximum response axis forwhich the direction is indicated by an arrow 1003. The secondmagnetoresistance element 1004 has a maximum response axis for which thedirection is indicated by an arrow 1005.

A first perturbing coil 1018 is disposed proximate to the firstmagnetoresistance element 1002. A second perturbing coil 1020 isdisposed proximate to the second magnetoresistance element 1004. Thefirst and second perturbing coils 1018, 1020 can be coupled in series.

A clock generator 1022 can be operable to generate a clock voltagesignal 1022 a coupled to a resistor 1024. A current signal 1024 a isgenerated as an end of the resistor 1024.

In response to the current signal 1024 a, the first perturbing coil 1018generates an AC magnetic field with directions indicated by an arrow1026. Also in response to the current signal 1024 a, the secondperturbing coil 1020 generates an AC magnetic field with directionsindicated by an arrow 1028. The directions 1026 of magnetic fieldsgenerated by the first perturbing coil 1018 are parallel to the maximumresponse axis 1003 of the first magnetoresistance element 1002. Thedirections 1028 of magnetic fields generated by the second perturbingcoil 1020 are parallel to the maximum response axis 1005 of the secondmagnetoresistance element 1004. Thus, the first magnetoresistanceelement 1002 and the second magnetoresistance element 1004 are directlyresponsive to magnetic fields generated by the first perturbing coil1018 and by the second and perturbing coil 1020, respectively. Thus, thefirst and second voltage signals 1002 a, 1004 a can be AC voltagesignals, each with a frequency equal to a frequency of the clock signal1022 a.

The magnetic field sensor 1000 may or may not include a currentconductor see, e.g., coils 1010, 1014), for example the currentconductor 501 of FIG. 5. In some embodiments, it should be understoodfrom discussion above that the current conductor can be a conductorinside of the magnetic field sensor 1000 and, in other embodiments, thecurrent conductor can be a conductor inside of the magnetic field sensor1000.

The current conductor is indicated in part by a first sensed currentcoil 1010 indicative of a first portion of, for example, a left side of,a sensed current conductor, for example, the left side of the sensedcurrent conductor 501 of FIG. 5. The sensed current conductor is alsoindicated in part by a second sensed current coil 1014 indicative of asecond portion of, for example, a right side of, the sensed the currentconductor, for example, the right side of the sensed current conductor501 of FIG. 5. However, it will be understood that the sensed currentconductor 501 is not coil. The first and second sensed current coils1010, 1014 are used merely to clarify that magnetic fields are generatedby the sensed current conductor 501.

As described above, a sensed current 501 carried by the sensed currentconductor 502 of FIG. 5, i.e., a sensed current 1009 carried by thefirst and second sensed current coils 1010, 1014, are described hereinto be DC currents, merely for clarity. Thus, the first sensed currentcoil 1010 generates a magnetic field with a first direction indicated byarrow 1012, and the second sensed current coil 1014 generates a magneticfield with a second direction indicated by an arrow 1016. The first andsecond directions 1012, 1016 are in opposite directions from each other.

For reasons described above in conjunction with FIGS. 4 and 5, themagnetic fields with first and second directions 1012, 1016,respectively, result in opposite direction changes of sensitivity of thefirst magnetoresistance element 1002 and of the second magnetoresistanceelement 1004. The changes of sensitivity are represented by the graphs800 of FIG. 8.

An amplifier 1030 is coupled to receive the first voltage signal 1002 a,which, as described above, can be an AC voltage signal like the signals802 a, 808 a, 814 a of FIG. 8, having an AC frequency equal to afrequency of the clock signal 1022 a, and having an amplitude inaccordance with an amplitude of the sensed magnetic field having thedirection 1012.

Similarly, an amplifier 1042 is coupled to receive the second voltagesignal 1004 a, which, as described above, can be an AC voltage signallike the signals 804 a, 810 a, 816 a of FIG. 8, having an AC frequencyequal to a frequency of the clock signal 1022 a, and having an amplitudein accordance with an amplitude of the sensed magnetic field having thedirection 1016.

The amplifier 1030 is operable to generate an amplified signal 1030 aand the amplifier 1042 is operable to generate and amplified signal 1042a.

The amplified signal 1030 a can be AC coupled with a capacitor 1032 andthe amplified signal 1042 a can be AC coupled with a capacitor 1044, togenerate AC coupled signals 1032 a, 1042 a.

A rectifier 1034 can be coupled to receive the AC coupled signal 1032 aand a rectifier 1046 can be coupled to receive the AC coupled signal1044 a. The rectifier 1034 can be operable to generate a rectifiedsignal 1034 a and the rectifier 1046 can be operable to generate arectified signal 1046 a. In some embodiments, the rectifiers 1034, 1046can be active rectifier circuits using feedback that have little or novoltage drop.

A filter 1036 can be coupled to receive the rectified signal 1034 a anda filter 1048 can be coupled to receive the rectified signal 1046 a. Insome embodiments, the filters 1036, 1048 can be low pass filters.

It will be understood that the rectifier 1034 coupled in series with thefilter 1036 forms a first amplitude detection circuit. It will also beunderstood that the rectifier 1046 series with the filter 1048 points asecond amplitude detection circuit. Thus, the filter 1036 is operable togenerate an amplitude signal 1036 a and the filter 1048 is operable togenerate an amplitude signal 1048 a.

Referring briefly to FIGS. 8 and 9, it should be understood that theamplitude detecting circuits result in signals in a first two rows ofgraphs 800 turning into signals in a first two rows of graphs 900.

The magnetic field sensor 1000 can also include an analog-to-digitalconverter 1038 coupled to receive the amplitude signal 1036 a and ananalog-to-digital converter 1050 to receive the amplitude signal 1048 a.The amplitude to digital converter 1038 is operable to generate aconverted signal 1038 a and the amplitude to digital converter 1050 isoff to generate a converted signal 1050 a.

The converted signals 1038 a, 1050 a can be received by a differencingcircuit 1040 operable to generate a difference signal 1040 a. Values ofthe difference signal are directly related to values of the measurecurrent 1009.

The magnetic field sensor 1000, which uses the perturbing magneticfields with directions 1026, 1028 to indirectly measure the sensedcurrent 1009 has advantages over a conventional magnetic field sensorthat directly measures the sensed current 1009. For example, because thecapacitors 1032, 1044 can block DC portions of signals to generate theAC coupled signals 1032 a, 1044 a, any undesirable effects that mayresult for undesirable DC offset voltages generated by the first andsecond magnetoresistance elements 1002, 1004 can be eliminated. This isan advantage both for GMR and TMR elements.

In addition, though the magnetic field sensor 1000 can use either TMRelements or GMR elements as the first and second magnetoresistanceelements 1002, 1004, the magnetic field sensor 1000 is well suited foruse of the TMR elements. It is known that TMR elements tend to havehigher sensitivities than GMR elements. It is also known that TMRelements tend to have worse electrical noise and worse signal to noiseratios at low frequencies that GMR elements. Because the magnetic fieldsensor 1000 actually operates with relatively high frequencies generatedby the clock signal generator 1022, the TMR elements, which have highersensitivity that GMR elements, can avoid the higher noise at lowfrequencies

The same advantages apply to all magnetic field sensors describedherein.

It will be understood that the magnetic field sensor 1000 is an openloop magnetic field sensor having no feedback loop from the differencesignal 1040 a to an earlier point in the magnetic field sensor 1000.FIG. 11 below describes a feedback magnetic field sensor with closedloop feedback.

The amplitude signals 1036 a, 1048 a are like the signals in the firsttwo rows of the graphs 900 of FIG. 9. The difference signal 1040 a islike the signals in the last row of the graph 900 of FIG. 9. Thus, thedifference signal 1040 a includes information about the amplitude of thesensed current 1009 and the direction of the sensed current 1009. Thesignal 1040 a can be sent outside of the magnetic field sensor 1000 forfurther processing and interpretation.

However, in other embodiments, the signal 1040 a can undergo furtherprocessing and interpretation by other circuits (not shown) within themagnetic field sensor.

The clock generator 1022 is shown to generate a two state clock signal1022 a. Thus, the current signal 1024 a is a two state current signaland the perturbing magnetic fields generated by the first and secondperturbing oils 1018, 1020 are two state magnetic fields. Accordingly,the signals 1002 a, 1004 a are two state signals. This is unlike the ACsinusoid signals of the graphs 100 FIG. 8. However, it will beunderstood that the same concepts apply to the graphs of FIGS. 8 and 9,but the signals in the graphs 800 of FIG. 8 will be square waves insteadof sinusoids.

In some other embodiments, the clocks signal generator 1022 is replacedby a sinewave generator.

The magnetic field sensor 1000, and all magnetic field sensor describedherein can provide a variety of advantages over conventional currentsensors used to directly sense magnetic fields due to current. Forexample, DC offsets and offset shifts of the TMR elements has little orno negative influence, because the capacitors 1032, 1044 can block DCsignal components.

Effects of any external stray fields are reduced. Effects of strayfields in the direction of the perturbing fields, i.e., in directionsperpendicular to directions 503 a, 503 b of FIG. 5, tend to be canceledby U=L-R calculation. However, stray fields in a direction perpendicularto the perturbing fields, i.e., in directions parallel to directions 503a, 503 b of FIG. 5 may be reduced, but by a lesser amount, dependingupon a strength of the stray fields. The closed loop mechanism describedbelow in conjunction with FIG. 11 can help to improve the lesser amountof improvement otherwise provided in the effect of stray fields indirections parallel to directions 503 a, 503 b of FIG. 5.

Referring now to FIG. 11, in which like elements of FIG. 11 are shownhaving like reference designations, another illustrative magnetic fieldsensor 1100 can include all of the elements of the magnetic field sensor1000 of FIG. 10.

The magnetic field sensor 1100 also can include a current driver 1102coupled to receive the difference signal 1040 a and operable to generatedifferential feedback current signal 1102 a, 1102 b. A first feedbackcoil 1108 can be disposed proximate to the first portion of the sensedcurrent conductor 1010. A second feedback coil 1110 can be disposedproximate to the second portion of the sensed current conductor 1014.

The differential feedback current signal 1102 a, 1102 b can be arrangedto generate a first feedback magnetic field that has a directionindicated by an arrow 1109 and to generate a second feedback magneticfield that has a direction indicated by and arrow 1111. The direction1109 opposes the direction 1012. The direction 1111 opposes thedirection 1016. The feedback results in the magnetic fields experiencedty the first and second magnetoresistance elements being approximatelyzero for all different values of the sensed current 1009.

The magnetic field sensor 1100 can also include a resistor 1104 inseries with one side of the differential current signal 1102 a, 1102 b.A voltage appears across the resistor 1104 with a value in accordancewith the differential current signal 1102 a, 1102 b. A differentialamplifier 1106 can be coupled to the resistor 1104. The amplifier 1106can generate and output signal that is indicative of the sensed current1009.

Advantages of the magnetic field sensor 1000 are described above inconjunction with FIG. 10. Further advantages are obtained in thefeedback arrangement of the magnetic field sensor 1100. In particular,it is known that magnetoresistance elements, both GMR and TMR elements,can suffer from being less than ideally linear throughout theiroperational range of magnetic fields. With a feedback arrangement,magnetic fields experienced by first and second magnetoresistanceelements 1002, 1004 can remain near zero magnetic field, thus, with afeedback arrangement, nonlinearity effects are eliminated or nearlyeliminated.

Further illustrative magnetic field sensors are described below. Somefurther examples of feedback arrangements are also described below.However, should be understood that all of the magnetic field sensorsdescribed herein can use a feedback arrangement like that described inconjunction with FIG. 11.

Read how to FIG. 12, in which like elements of FIG. 10 are shown havinglike reference designations, another illustrative magnetic field sensor1200 can include most of the elements of the magnetic field sensor 1000of FIG. 10. However, in the magnetic fields sensor 1200, rectifiercircuits 1034, 1046 are not used, but are replaced by demodulatorcircuits 1202, 1204.

The demodulator circuit 1202 is coupled to receive the AC coupled signal1032 and also coupled to receive the clock signal 1022. The demodulatorcircuit 1202 can be operable to switch back and forth between the ACcoupled signal 1032 a and an inverted version of the AC coupled signal1032 a. The clock signal 1022 a can be the same frequency as the ACcoupled signal 1032 a. Thus, the demodulator circuit 1202 can beoperable to generate a rectified signal 1202 a, which can be the same asor similar to the rectified signal 1034 a of FIG. 10.

The demodulator circuit 1204 is similarly coupled as the demodulatorcircuit 1202 and operates in the same way.

Referring now to FIG. 13, in which like elements of FIG. 10 are shownhaving like reference designations, another illustrative magnetic fieldsensor 1300 can include many of the elements of the magnetic fieldsensor 1000 of FIG. 10. Unlike the first and second magnetoresistanceelements 1002, 1004 of FIG. 10, the magnetic field sensor 1300 caninclude first and second bridge circuits.

The first bridge circuit can include a first magnetoresistance element1302 and a second magnetoresistance element 1304 coupled together with afirst fixed resistor 1306 and a second fixed resistor 1308. The firstbridge circuit is operable to generate a first differential bridgesignal 1312, 1314.

The second bridge circuit can include a third magnetoresistance element1316 and a fourth magnetoresistance element 1318 coupled together with athird fixed resistor 1320 and a fourth fixed resistor 1322. The secondbridge circuit is operable to generate a second differential bridgesignal 1324, 1326.

The first magnetoresistance element 1302 can have maximum response axisof the direction indicated by an arrow 1303. The secondmagnetoresistance element 1304 can have a maximum response axis of thedirection indicated by an arrow 1305. The third magnetoresistanceelement 1316 can have a maximum response axis of the direction indicatedby an arrow 1317. The fourth magnetoresistance element 1318 can have amaximum response axis of the direction indicated by an arrow 1319.

The first and second magnetoresistance elements 1302, 1304 can both bedisposed proximate to each other and on the left side, for example,proximate to the left side of the current conductor 502 of FIG. 5. Thethird and fourth magnetoresistance elements 1316, 1318 can both bedisposed proximate to each other and on the right side, for example,proximate to the right side of the current conductor 502 of FIG. 5.

The first sensed current conductor 1010, i.e., the left side of thecurrent conductor 502 of FIG. 5, can be disposed proximate to the firstand second magnetoresistance elements 1302, 1304. The second sensedcurrent conductor 1014, i.e., the right side of the current conductor502 of FIG. 5, can be disposed proximate to the third and fourthmagnetoresistance elements 1316, 1318.

Also unlike the first and second perturbing coils 1018, 1020 of FIG. 10,the magnetic field sensor 1300 can include first, second, third, andfourth perturbing coils 1332, 1334, 1336, 1338, respectively. The firstperturbing coil 1332 can beast disposed proximate to the firstmagnetoresistance element 1302. The second perturbing coil 1334 can bedisposed proximate to the second magnetoresistance element 1304. Thethird perturbing coil 1336 can beast disposed proximate to the thirdmagnetoresistance element 1316. The fourth perturbing coil 1338 can bedisposed proximate to the fourth magnetoresistance element 1318.

The first, second, third, and fourth perturbing coils 1332, 1334, 1336,1338 can each generate AC magnetic fields with directions indicated byan arrow 1329. The directions indicated by the arrow 1329 are parallelto the maximum response axes 1303, 1305, 1317, 1319.

The magnetic field sensor 1300 can operate in much the same way as thatdescribed above for the magnetic field sensor 1000 of FIG. 10.Therefore, operational the magnetic field sensor 1300 is not describedin detail herein.

Referring now to FIG. 1400, in which like elements of FIGS. 7, 10, and13 are shown having like reference designations, another illustrativemagnetic field sensor 1400 can have many characteristics that aresimilar to the magnetic field sensors 1000, 1200, and 1300 of FIGS. 10,12, and 14.

The magnetic field sensor 1400 can include four magnetoresistanceelements coupled together in a full bridge arrangement 700, which can bethe same as or similar to the full bridge arrangement 700 of FIG. 7.

First and second magnetoresistance elements, La, Lb can both be disposedproximate to each other and on the left side, for example, on the leftside of the current conductor 502 of FIG. 5. Third and fourthmagnetoresistance elements Ra, Rb can both be disposed proximate to eachother and on the right side, for example, on the right side of thecurrent conductor 502 of FIG. 5.

The first perturbing coil 1332 can be disposed proximate to the firstmagnetoresistance element, La, the second perturbing coil 1334 can bedisposed proximate to the second magnetoresistance element, Lb, thethird perturbing coil 1336 can be disposed proximate to the thirdmagnetoresistance element, Ra, and the fourth perturbing coil 1338 canbe disposed proximate to the fourth magnetoresistance element, Rb.

Taken together the first, second, third, and fourth perturbing coils1332, 1334, 1336, 1338 along with the clock signal generator 1022 andthe resistor 1330 are referred to herein as a perturbing magnetic fieldsignal generator 1401.

The difference signal 712 a, like the difference signal 712 a of FIG. 7,is already a signal that represents a difference of signals generated bymagnetoresistance elements on the left and right sides, for example leftand right sides of the current conductor 502 of FIG. 5. Thus, twocircuit channels for left and right sides described in conjunction withmagnetic field sensors of FIGS. 10, 11, 12, and 13, are not required.

The difference signal 712 a can be received by a capacitor 1424, whichcan be coupled to a demodulator 1426, which can be coupled to a filter1428, which can be coupled to an analog-to-digital converter 1410 togenerate a digital signal 1410 a. The demodulator 1426 and the filter1428 form an amplitude detecting circuit as described above inconjunction with FIG. 12.

Values of the digital signal 1410 a can be indicative of values of thesensed current signal 1009.

Referring now to FIG. 15, in which like elements of FIGS. 7, 10, 11, and14 are shown having like reference designations a magnetic field sensor1500 can be similar to the magnetic field sensor 1400 and FIG. 14 butalso having a feedback arrangement of magnetic field sensor 1100 of FIG.11.

Thus, the magnetic field sensor 1500 also can include a current driver1502 coupled to the filter 1428 and operable to generate differentialfeedback current signal 1502 a, 1502 b received by the first and secondfeedback coils 1108, 1110 described above in conjunction with FIG. 11.

The magnetic field sensor 1500 can also include a resistor 1503 inseries with one side of the differential current signal 1502 a, 1502 b.A voltage appears across the resistor 1503 with a value in accordancewith the differential current signal 1502 a, 1502 b. A differentialamplifier 1504 can be coupled to the resistor 1503. The differentialamplifier 1506 can be operable to generate a signal 1504 a, values ofwhich can be indicative of the sensed current signal 1009. The signal1504 a can be coupled to an analog-to-digital converter 1506 can beoperable to generate a digital signal 1506 a, which can also beindicative of the sensed current signal 1009.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that the scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

Elements of embodiments described herein may be combined to form otherembodiments not specifically set forth above. Various elements, whichare described in the context of a single embodiment, may also beprovided separately or in any suitable subcombination. Other embodimentsnot specifically described herein are also within the scope of thefollowing claims.

What is claimed is:
 1. A magnetic field sensor, comprising: a firstmagnetoresistance element having a first maximum response axis andhaving a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis; a secondmagnetoresistance element having a second maximum response axis parallelto the first maximum response axis and having a second pinning layerwith a second magnetic direction perpendicular to the second maximumresponse axis; a first magnetic field generator disposed proximate tothe first magnetoresistance element, the first magnetic field generatorconfigured to generate a first AC magnetic field experienced by thefirst magnetoresistance element and parallel to the first maximumresponse axis; and a second magnetic field generator disposed proximateto the second magnetoresistance element, the second magnetic fieldgenerator configured to generate a second AC magnetic field experiencedby the second magnetoresistance element and parallel to the secondmaximum response axis, wherein the magnetic field sensor is responsiveto a sensed current passing through a current conductor, the currentconductor comprising: a first current conductor portion disposedproximate to the first magnetoresistance element; and a second currentconductor portion disposed proximate to the second magnetoresistanceelement, wherein the first current conductor portion is configured togenerate a first current conductor magnetic field experienced by thefirst magnetoresistance element in response to the sensed currentpassing through the current conductor, wherein the second currentconductor portion is configured to generate a second current conductormagnetic field experienced by the second magnetoresistance element inresponse to the sensed current passing through the current conductor,wherein the first current conductor magnetic field is perpendicular tothe first maximum response axis, and wherein the second currentconductor magnetic field is perpendicular to the second maximum responseaxis, wherein magnetic field sensor further comprises: a feedbackconductor having a first feedback conductor portion disposed proximateto the first current conductor portion and having a second feedbackconductor portion disposed proximate to the second current conductorportion, wherein the feedback conductor is configured to generate firstand second feedback conductor magnetic fields in response to a feedbackcurrent passing through the feedback conductor, wherein the first andsecond feedback conductor magnetic fields are parallel to and opposingthe first and second current conductor magnetic fields, respectively. 2.The magnetic field sensor of claim 1, further comprising: a substrateholding the first magnetoresistance element, the secondmagnetoresistance element, the first magnetic field generator, and thesecond magnetic field generator; and a lead frame having a plurality ofleads, wherein the current conductor forms a current path between two ofthe plurality of leads.
 3. The magnetic field sensor of claim 2, whereinthe current conductor comprises an open loop such that the current flowsin a first direction at a first one of the two of the plurality of leadsand flows in a second direction different than the first direction at asecond different one of the two of the plurality of leads.
 4. Themagnetic field sensor of claim 1, wherein the first magnetoresistanceelement comprises a first TMR element and the second magnetoresistanceelement comprises a second TMR element.
 5. The magnetic field sensor ofclaim 1, further comprising: a first amplitude detecting circuitoperable to detect a first amplitude of a first signal generated inresponse to the first magnetoresistance element; a second amplitudedetecting circuit operable to detect a second amplitude of a secondsignal generated in response to the second magnetoresistance element;and a differencing circuit operable to generate a difference of thefirst and second amplitudes.
 6. The magnetic field sensor of claim 5,wherein the difference is indicative of an amplitude and a direction ofthe sensed current.
 7. The magnetic field sensor of claim 5, wherein thefirst amplitude detecting circuit comprises a first rectifier circuitcoupled to a first filter and wherein the second amplitude detectingcircuit comprises a second rectifier circuit coupled to a second filter.8. The magnetic field sensor of claim 5, wherein the first amplitudedetecting circuit comprises a first demodulator and wherein the secondamplitude detecting circuit comprises a second demodulator.
 9. Themagnetic field sensor of claim 1, further comprising: a thirdmagnetoresistance element having a third maximum response axis andhaving a third pinning layer with a third magnetic directionperpendicular to the third maximum response axis; a fourthmagnetoresistance element having a fourth maximum response axis andhaving a fourth pinning layer with a fourth magnetic directionperpendicular to the fourth maximum response axis.
 10. The magneticfield sensor of claim 9, further comprising: a third magnetic fieldgenerator disposed proximate to the third magnetoresistance element, thethird magnetic field generator configured to generate an AC magneticfield experienced by the third magnetoresistance element and parallel tothe third maximum response axis; and a fourth magnetic field generatordisposed proximate to the fourth magnetoresistance element, the fourthmagnetic field generator configured to generate a fourth AC magneticfield experienced by the fourth magnetoresistance element and parallelto the fourth maximum response axis.
 11. The magnetic field sensor ofclaim 10, wherein the current conductor further comprises: a thirdcurrent conductor portion disposed proximate to the thirdmagnetoresistance element; and a fourth current conductor portiondisposed proximate to the fourth magnetoresistance element, wherein thethird current conductor portion is configured to generate a thirdcurrent conductor magnetic field experienced by the thirdmagnetoresistance element in response to a sensed current passingthrough the current conductor, wherein the fourth current conductorportion is configured to generate a fourth current conductor magneticfield experienced by the fourth magnetoresistance element in response toa sensed current passing through the current conductor, wherein thethird current conductor magnetic field is parallel to the third magneticdirection of the third pinning layer, and wherein the fourth currentconductor magnetic field parallel to the fourth magnetic direction ofthe fourth pinning layer.
 12. The magnetic field sensor of claim 9,wherein the first magnetoresistance element and the secondmagnetoresistance element are coupled in a first full bridge with firstand second fixed resistors, and wherein the third and fourthmagnetoresistance elements are coupled in a second full bridge withthird and fourth fixed resistors.
 13. The magnetic field sensor of claim12, wherein the first magnetoresistance element comprises a first TMRelement, the second magnetoresistance element comprises a second TMRelement, the third magnetoresistance element comprises a third TMRelement and the fourth magnetoresistance element comprises a fourth TMRelement.
 14. The magnetic field sensor of claim 12, further comprising:a first amplitude detecting circuit operable to detect a first amplitudeof a first signal generated in response to the first full bridge; asecond amplitude detecting circuit operable to detect a second amplitudeof a second signal generated in response to the second full bridge; anda differencing circuit operable to generate a difference of the firstand second amplitudes, wherein the difference is indicative of anamplitude and a direction of the current.
 15. A magnetic field sensor,comprising: a first magnetoresistance element having a first maximumresponse axis and having a first pinning layer with a first magneticdirection perpendicular to the first maximum response axis; a secondmagnetoresistance element having a second maximum response axis parallelto the first maximum response axis and having a second pinning layerwith a second magnetic direction perpendicular to the second maximumresponse axis; a first magnetic field generator disposed proximate tothe first magnetoresistance element, the first magnetic field generatorconfigured to generate a first AC magnetic field experienced by thefirst magnetoresistance element and parallel to the first maximumresponse axis; a second magnetic field generator disposed proximate tothe second magnetoresistance element, the second magnetic fieldgenerator configured to generate a second AC magnetic field experiencedby the second magnetoresistance element and parallel to the secondmaximum response axis, a third magnetoresistance element having a thirdmaximum response axis and having a third pinning layer with a thirdmagnetic direction perpendicular to the third maximum response axis; afourth magnetoresistance element having a fourth maximum response axisand having a fourth pinning layer with a fourth magnetic directionperpendicular to the fourth maximum response axis, wherein the magneticfield sensor is responsive to a sensed current passing through a currentconductor, wherein the first magnetoresistance element and the secondmagnetoresistance element are coupled in a first full bridge with firstand second fixed resistors, and wherein the third and fourthmagnetoresistance elements are coupled in a second full bridge withthird and fourth fixed resistors, the current conductor comprising: afirst current conductor portion disposed proximate to the firstmagnetoresistance element; and a second current conductor portiondisposed proximate to the second magnetoresistance element, wherein thefirst current conductor portion is configured to generate a firstcurrent conductor magnetic field experienced by the firstmagnetoresistance element in response to the sensed current passingthrough the current conductor, wherein the second current conductorportion is configured to generate a second current conductor magneticfield experienced by the second magnetoresistance element in response tothe sensed current passing through the current conductor, wherein thefirst current conductor magnetic field is perpendicular to the firstmaximum response axis, and wherein the second current conductor magneticfield is perpendicular to the second maximum response axis, the magneticfield sensor further comprising: a first amplitude detecting circuitoperable to detect a first amplitude of a first signal generated inresponse to the first full bridge; a second amplitude detecting circuitoperable to detect a second amplitude of a second signal generated inresponse to the second full bridge; and a differencing circuit operableto generate a difference of the first and second amplitudes, wherein thedifference is indicative of an amplitude and a direction of the current,wherein the first amplitude detecting circuit comprises a firstrectifier coupled to a first filter, and wherein the second amplitudedetecting circuit comprises a second rectifier circuit coupled to asecond filter.
 16. The magnetic field sensor of claim 15, furthercomprising: a feedback conductor comprising: a first feedback conductorportion disposed proximate to the first current conductor portion andhaving a second feedback conductor portion disposed proximate to thesecond current conductor portion, wherein the feedback conductor isconfigured to generate first and second feedback conductor magneticfields in response to a feedback current passing through the feedbackconductor, wherein the first and second feedback conductor magneticfields are parallel to and opposing the first and second currentconductor magnetic fields, respectively.
 17. The magnetic the magneticfield sensor of claim 15, further comprising: a substrate holding thefirst magnetoresistance element, the second magnetoresistance element,the third magnetoresistance element, the fourth magnetoresistanceelement, the first magnetic field generator, and the second magneticfield generator; and a lead frame having a plurality of leads, whereinthe current conductor forms a current path between two of the pluralityof leads.
 18. The magnetic field sensor of claim 17, wherein the currentconductor comprises an open loop such that the current flows in a firstdirection at a first one of the two of the plurality of leads and flowsin a second direction different than the first direction at a seconddifferent one of the two of the plurality of leads.
 19. The magneticfield sensor of claim 15, wherein the first magnetoresistance elementcomprises a first TMR element, the second magnetoresistance elementcomprises a second TMR element, the third magnetoresistance elementcomprises a third TMR element and the fourth magnetoresistance elementcomprises a fourth TMR element.
 20. A magnetic field sensor, comprising:a first magnetoresistance element having a first maximum response axisand having a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis; a secondmagnetoresistance element having a second maximum response axis parallelto the first maximum response axis and having a second pinning layerwith a second magnetic direction perpendicular to the second maximumresponse axis; a first magnetic field generator disposed proximate tothe first magnetoresistance element, the first magnetic field generatorconfigured to generate a first AC magnetic field experienced by thefirst magnetoresistance element and parallel to the first maximumresponse axis; a second magnetic field generator disposed proximate tothe second magnetoresistance element, the second magnetic fieldgenerator configured to generate a second AC magnetic field experiencedby the second magnetoresistance element and parallel to the secondmaximum response axis, a third magnetoresistance element having a thirdmaximum response axis and having a third pinning layer with a thirdmagnetic direction perpendicular to the third maximum response axis; afourth magnetoresistance element having a fourth maximum response axisand having a fourth pinning layer with a fourth magnetic directionperpendicular to the fourth maximum response axis, wherein the magneticfield sensor is responsive to a sensed current passing through a currentconductor, wherein the first magnetoresistance element and the secondmagnetoresistance element are coupled in a first full bridge with firstand second fixed resistors, and wherein the third and fourthmagnetoresistance elements are coupled in a second full bridge withthird and fourth fixed resistors, the current conductor comprising: afirst current conductor portion disposed proximate to the firstmagnetoresistance element; and a second current conductor portiondisposed proximate to the second magnetoresistance element, wherein thefirst current conductor portion is configured to generate a firstcurrent conductor magnetic field experienced by the firstmagnetoresistance element in response to the sensed current passingthrough the current conductor, wherein the second current conductorportion is configured to generate a second current conductor magneticfield experienced by the second magnetoresistance element in response tothe sensed current passing through the current conductor, wherein thefirst current conductor magnetic field is perpendicular to the firstmaximum response axis, and wherein the second current conductor magneticfield is perpendicular to the second maximum response axis, the magneticfield sensor further comprising: a first amplitude detecting circuitoperable to detect a first amplitude of a first signal generated inresponse to the first full bridge; a second amplitude detecting circuitoperable to detect a second amplitude of a second signal generated inresponse to the second full bridge; and a differencing circuit operableto generate a difference of the first and second amplitudes, wherein thedifference is indicative of an amplitude and a direction of the current,wherein the first amplitude detecting circuit comprises a firstdemodulator, and wherein the second amplitude detecting circuitcomprises a second demodulator.
 21. The magnetic field sensor of claim20, wherein the first magnetoresistance element comprises a first TMRelement, the second magnetoresistance element comprises a second TMRelement, the third magnetoresistance element comprises a third TMRelement and the fourth magnetoresistance element comprises a fourth TMRelement.
 22. The magnetic field sensor of claim 20, further comprising:a feedback conductor comprising: a first feedback conductor portiondisposed proximate to the first current conductor portion and having asecond feedback conductor portion disposed proximate to the secondcurrent conductor portion, wherein the feedback conductor is configuredto generate first and second feedback conductor magnetic fields inresponse to a feedback current passing through the feedback conductor,wherein the first and second feedback conductor magnetic fields areparallel to and opposing the first and second current conductor magneticfields, respectively.
 23. The magnetic the magnetic field sensor ofclaim 20, further comprising: a substrate holding the firstmagnetoresistance element, the second magnetoresistance element, thethird magnetoresistance element, the fourth magnetoresistance element,the first magnetic field generator, and the second magnetic fieldgenerator; and a lead frame having a plurality of leads, wherein thecurrent conductor forms a current path between two of the plurality ofleads.
 24. The magnetic field sensor of claim 23, wherein the currentconductor comprises an open loop such that the current flows in a firstdirection at a first one of the two of the plurality of leads and flowsin a second direction different than the first direction at a seconddifferent one of the two of the plurality of leads.
 25. The magneticfield sensor of claim 20, wherein the first magnetoresistance elementcomprises a first TMR element, the second magnetoresistance elementcomprises a second TMR element, the third magnetoresistance elementcomprises a third TMR element and the fourth magnetoresistance elementcomprises a fourth TMR element.
 26. A magnetic field sensor, comprising:a first magnetoresistance element having a first maximum response axisand having a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis; a secondmagnetoresistance element having a second maximum response axis parallelto the first maximum response axis and having a second pinning layerwith a second magnetic direction perpendicular to the second maximumresponse axis; a first magnetic field generator disposed proximate tothe first magnetoresistance element, the first magnetic field generatorconfigured to generate a first AC magnetic field experienced by thefirst magnetoresistance element and parallel to the first maximumresponse axis; a second magnetic field generator disposed proximate tothe second magnetoresistance element, the second magnetic fieldgenerator configured to generate a second AC magnetic field experiencedby the second magnetoresistance element and parallel to the secondmaximum response axis, a third magnetoresistance element having a thirdmaximum response axis and having a third pinning layer with a thirdmagnetic direction perpendicular to the third maximum response axis; afourth magnetoresistance element having a fourth maximum response axisand having a fourth pinning layer with a fourth magnetic directionperpendicular to the fourth maximum response axis, wherein the first,second, third and fourth magnetoresistance elements are coupled togetherin a full bridge; and an amplitude detecting circuit operable to detectan amplitude of a signal generated in response to the full bridge,wherein the magnetic field sensor is responsive to a sensed currentpassing through a current conductor, and wherein the amplitude detectingcircuit comprises a rectifier coupled to a filter.
 27. The magneticfield sensor of claim 26, wherein the first magnetoresistance elementcomprises a first TMR element, the second magnetoresistance elementcomprises a second TMR element, the third magnetoresistance elementcomprises a third TMR element and the fourth magnetoresistance elementcomprises a fourth TMR element.
 28. The magnetic field sensor of claim26, further comprising: a third magnetic field generator disposedproximate to the third magnetoresistance element, the third magneticfield generator configured to generate an AC magnetic field experiencedby the third magnetoresistance element and parallel to the third maximumresponse axis; and a fourth magnetic field generator disposed proximateto the fourth magnetoresistance element, the fourth magnetic fieldgenerator configured to generate a fourth AC magnetic field experiencedby the fourth magnetoresistance element and parallel to the fourthmaximum response axis.
 29. The magnetic field sensor of claim 28,wherein the current conductor comprises: a first current conductorportion disposed proximate to the first magnetoresistance element; and asecond current conductor portion disposed proximate to the secondmagnetoresistance element, wherein the first current conductor portionis configured to generate a first current conductor magnetic fieldexperienced by the first magnetoresistance element in response to thesensed current passing through the current conductor, wherein the secondcurrent conductor portion is configured to generate a second currentconductor magnetic field experienced by the second magnetoresistanceelement in response to the sensed current passing through the currentconductor, wherein the first current conductor magnetic field isperpendicular to the first maximum response axis, and wherein the secondcurrent conductor magnetic field is perpendicular to the second maximumresponse axis.
 30. The magnetic field sensor of claim 29, wherein thecurrent conductor further comprises: a third current conductor portiondisposed proximate to the third magnetoresistance element; and a fourthcurrent conductor portion disposed proximate to the fourthmagnetoresistance element, wherein the third current conductor portionis configured to generate a third current conductor magnetic fieldexperienced by the third magnetoresistance element in response to asensed current passing through the current conductor, wherein the fourthcurrent conductor portion is configured to generate a fourth currentconductor magnetic field experienced by the fourth magnetoresistanceelement in response to a sensed current passing through the currentconductor, wherein the third current conductor magnetic field isparallel to the third magnetic direction of the third pinning layer, andwherein the fourth current conductor magnetic field parallel to thefourth magnetic direction of the fourth pinning layer.
 31. A magneticfield sensor, comprising: a first magnetoresistance element having afirst maximum response axis and having a first pinning layer with afirst magnetic direction perpendicular to the first maximum responseaxis; a second magnetoresistance element having a second maximumresponse axis parallel to the first maximum response axis and having asecond pinning layer with a second magnetic direction perpendicular tothe second maximum response axis; a first magnetic field generatordisposed proximate to the first magnetoresistance element, the firstmagnetic field generator configured to generate a first AC magneticfield experienced by the first magnetoresistance element and parallel tothe first maximum response axis; a second magnetic field generatordisposed proximate to the second magnetoresistance element, the secondmagnetic field generator configured to generate a second AC magneticfield experienced by the second magnetoresistance element and parallelto the second maximum response axis, a third magnetoresistance elementhaving a third maximum response axis and having a third pinning layerwith a third magnetic direction perpendicular to the third maximumresponse axis; a fourth magnetoresistance element having a fourthmaximum response axis and having a fourth pinning layer with a fourthmagnetic direction perpendicular to the fourth maximum response axis,wherein the first, second, third and fourth magnetoresistance elementsare coupled together in a full bridge; and an amplitude detectingcircuit operable to detect an amplitude of a signal generated inresponse to the full bridge, wherein the magnetic field sensor isresponsive to a sensed current passing through a current conductor, andwherein the amplitude detecting circuit comprises a demodulator.
 32. Themagnetic field sensor of claim 31, wherein the first magnetoresistanceelement comprises a first TMR element, the second magnetoresistanceelement comprises a second TMR element, the third magnetoresistanceelement comprises a third TMR element and the fourth magnetoresistanceelement comprises a fourth TMR element.
 33. The magnetic field sensor ofclaim 31, further comprising: a third magnetic field generator disposedproximate to the third magnetoresistance element, the third magneticfield generator configured to generate an AC magnetic field experiencedby the third magnetoresistance element and parallel to the third maximumresponse axis; and a fourth magnetic field generator disposed proximateto the fourth magnetoresistance element, the fourth magnetic fieldgenerator configured to generate a fourth AC magnetic field experiencedby the fourth magnetoresistance element and parallel to the fourthmaximum response axis.
 34. The magnetic field sensor of claim 33,wherein the current conductor comprises: a first current conductorportion disposed proximate to the first magnetoresistance element; and asecond current conductor portion disposed proximate to the secondmagnetoresistance element, wherein the first current conductor portionis configured to generate a first current conductor magnetic fieldexperienced by the first magnetoresistance element in response to thesensed current passing through the current conductor, wherein the secondcurrent conductor portion is configured to generate a second currentconductor magnetic field experienced by the second magnetoresistanceelement in response to the sensed current passing through the currentconductor, wherein the first current conductor magnetic field isperpendicular to the first maximum response axis, and wherein the secondcurrent conductor magnetic field is perpendicular to the second maximumresponse axis.
 35. The magnetic field sensor of claim 34, wherein thecurrent conductor further comprises: a third current conductor portiondisposed proximate to the third magnetoresistance element; and a fourthcurrent conductor portion disposed proximate to the fourthmagnetoresistance element, wherein the third current conductor portionis configured to generate a third current conductor magnetic fieldexperienced by the third magnetoresistance element in response to asensed current passing through the current conductor, wherein the fourthcurrent conductor portion is configured to generate a fourth currentconductor magnetic field experienced by the fourth magnetoresistanceelement in response to a sensed current passing through the currentconductor, wherein the third current conductor magnetic field isparallel to the third magnetic direction of the third pinning layer, andwherein the fourth current conductor magnetic field parallel to thefourth magnetic direction of the fourth pinning layer.
 36. A method ofproviding a magnetic field sensor, comprising: generating a first ACmagnetic field experienced by a first magnetoresistance element andparallel to a first maximum response axis, the first magnetoresistanceelement having the first maximum response axis and having a firstpinning layer with a first magnetic direction perpendicular to the firstmaximum response axis; generating a second AC magnetic field experiencedby a second magnetoresistance element and parallel to a second maximumresponse axis, the second magnetoresistance element having the secondmaximum response axis parallel to the first maximum response axis andhaving a second pinning layer with a second magnetic directionperpendicular to the second maximum response axis; generating a firstcurrent conductor magnetic field experienced by the firstmagnetoresistance element in response to a sensed current passingthrough a current conductor; generating a second current conductormagnetic field experienced by the second magnetoresistance element inresponse to the sensed current passing through the current conductor,wherein the first current conductor magnetic field is perpendicular tothe first maximum response axis, and wherein the second currentconductor magnetic field is perpendicular to the second maximum responseaxis; and generating first and second feedback conductor magnetic fieldsin response to a feedback current passing through a feedback conductor,wherein the first and second feedback conductor magnetic fields areparallel to and opposing the first and second current conductor magneticfields, respectively.
 37. A magnetic field sensor, comprising: means forgenerating a first AC magnetic field experienced by a firstmagnetoresistance element and parallel to a first maximum response axis,the first magnetoresistance element having the first maximum responseaxis and having a first pinning layer with a first magnetic directionperpendicular to the first maximum response axis; means for generating asecond AC magnetic field experienced by a second magnetoresistanceelement and parallel to a second maximum response axis, the secondmagnetoresistance element having the second maximum response axisparallel to the first maximum response axis and having a second pinninglayer with a second magnetic direction perpendicular to the secondmaximum response axis; means for generating a first current conductormagnetic field experienced by the first magnetoresistance element inresponse to a sensed current passing through a current conductor; meansfor generating a second current conductor magnetic field experienced bythe second magnetoresistance element in response to the sensed currentpassing through the current conductor, wherein the first currentconductor magnetic field is perpendicular to the first maximum responseaxis, and wherein the second current conductor magnetic field isperpendicular to the second maximum response axis; and means forgenerating first and second feedback conductor magnetic fields inresponse to a feedback current passing through a feedback conductor,wherein the first and second feedback conductor magnetic fields areparallel to and opposing the first and second current conductor magneticfields, respectively.